WASHINGTON  U.S. Interior Secretary Ken Salazar plans to leave his cabinet post by the end of March, an administration official said on condition of anonymity in advance of a formal announcement.

Salazar, 57, plans to return to Colorado, according to the Denver Post, which reported his departure plans earlier Wednesay. He represented the state in the U.S. Senate before joining President Barack Obama’s administration in 2009.

Salazar’s four years in office included supervising the U.S. response to the 2010 BP PLC oil spill in the Gulf of Mexico, promoting solar-energy projects and expanding oil and gas exploration off Alaska’s coast.

He’s the latest cabinet secretary to leave as Obama begins his second, four-year term on Jan. 20.